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Parallel rays of light of intensity `I=912 WM^-2` are incident on a spherical black body kept in surroundings of temperature 300K. Take Stefan-Boltzmann constant `sigma=5.7xx10^-8` `Wm^-2K^-4` and assume that the energy exchange with the surroundings is only through radiation. The final steady state temperature of the black body is close toA. `330 K`B. `660 K`C. `990 K`D. `1550 K` |
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Answer» Correct Answer - A In steady state `I piR^(2) = sigma (T^(4) -T_(0)^(4)) 4pi R^(2)` `rArr I = sigma (T^(4)-T_(0)^(4)) 4 rArr T^(4) -T_(0)^(4) = 40 xx 10^(6)` `rArr T^(4) - 81 xx 10^(8) xx 40 xx 10^(8) rArr T^(4) = 121 xx 10^(8)` `rArr T ~~ 330 K` |
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